The invention lies in the field of controlling the operation of a complex system.
It applies particularly, but not exclusively, to controlling an engine.
In general, regulated complex systems respond to external setpoints, with a regulation relationship adjusting internal operating variables that tend to bring the system to the operating point that complies with the setpoint, and to keep it there.
For example, with an engine, an increasing thrust setpoint has as its first effect an increase in the variable that is representative of pressure in the combustion chamber of the engine.
In order to regulate a complex system, it is known to use a setpoint that is filtered by a first order filter, as shown in FIG. 1A.
In this example, the filtered setpoint C* is obtained from the setpoint C by applying equation (1) below, in which the gain K represents the dynamic speed of the filter and C*n-1 is a preceding value of the filtered setpoint:C*=K×(C−C*n-1)+C*n-1  (1)
In FIG. 1A, references 21, 24, and 25 designate respectively: a subtracter; an adder; and a delay; all three of which are known to the person skilled in the art.
Furthermore, complex systems usually include subsystems having internal parameters that need to be kept below respective operating limits, regardless of the operating conditions desired of the system.
For example, in an engine, the speed of rotation of a turbine must never exceed a predetermined limit value.
Conflicts can therefore arise between the need to comply with the operating limits of a subsystem and the objective of responding to the setpoints.
These conflicts can arise in particular due to poor knowledge of the utilization ranges while designing the system, or to drift over time in certain characteristics of the system.
In an attempt to mitigate this problem, the prior art proposes systems such as that shown in FIG. 1B, in which a saturator 26 is used for limiting the speed at which operating points change, and a saturator 27 is used to limit amplitude.
A saturator SAT concerning the rate at which a setpoint can change is applied to the parameter K×(C−C*n-1), where the value of the filtered setpoint C* is obtained using equation (2) below:C*=SAT(K×(C−C*n-1))+C*n-1  (2)
It is also possible to use a second saturator concerning the rate at which a setpoint can change, with the value of the filtered setpoint C* then being obtained by equation (3):C*=SAT(SAT(K×(C−C*n-1))+C*n-1)  (3)
However, that solution is unsatisfactory since although it enables the rate of change of operating points to be slowed down while tending towards the setpoint, and although it enables the setpoint to be limited, it does not in any way guarantee that critical parameters of the subsystems are kept within their own operating limits.